Hall effect measurement instrument with temperature compensation

ABSTRACT

Disclosed is a Hall Effect instrument with the capability of compensating for temperature drift consistently, accurately and in real time of operation. The instrument embodies a four-point ohmmeter circuit measuring Hall Effect sensor resistance and tracking the effect of temperature on the Hall Effect sensor. The instrument takes into account a relationship between the temperature and a temperature compensation index on a per probe basis, which has exhibited a deterministic difference observed by the present inventor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of co-pending U.S.application Ser. No. 14/077,322 entitled A HALL EFFECT MEASUREMENTDEVICE WITH TEMPERATURE COMPENSATION and filed Nov. 12, 2013, which isherein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to non-destructive testing andnon-destructive instruments (NDT/NDI) and more particularly to a HallEffect probe and measurement device with compensation of measurementdrift caused by temperature change.

BACKGROUND OF THE INVENTION

Hall Effect sensors have been used in measurement devices such asthickness gages (e.g. Olympus NDT Magna Mike 8500) to accurately measurethickness of nonferrous materials. One of the most often seenapplications is thickness measurement on plastic bottles. A Hall Effectsensor typically comprises a probe that has magnet(s) generating aprimary magnetic field. Measurements are performed by holding thedevice's magnetic probe to one surface of the test material and placinga small steel target ball on the opposite surface. The target ball, inresponding to the primary magnetic field, generates a secondary magneticfield, which varies according to the distance between the probe and thesteel target ball. A Hall-effect sensor, which measures the strength ofthe secondary magnetic field, built into the probe measures the distancebetween the probe tip and target ball. Typically measurements areinstantly displayed as easy-to-read digital readings on the devicedisplay panel.

One unique challenge encountered and overcome by the present disclosureinvolves a hall sensor that is not part of an integrated circuit onboard the instrument. As required by many Hall Effect instruments orapplications, a major portion of the circuitry is assembled on the mainbody of the instrument, which is coupled to the Hall Effect sensor orprobe via wires or cables with a length that meets the operator's needs,e.g. 1 meter. This physical distance between the Hall Effect sensor andthe instrument presents an unknown wiring and connector resistance. Asthe Hall Effect sensor is located in the probe and sensitive totemperature changes, it presents a unique challenge for the instrumentto compensate the temperature of the probe assembly including bothmagnetic parts and the Hall effect sensor.

It also presents more unique challenges when the operation of a Halleffect sensor based instrument involves interchange of Hall sensorprobes and gage and maintaining an accurate and temperature compensatedsystem.

However, it's been widely observed that the accuracy of a measurementfrom a Hall effect thickness gage drifts with temperature quitenoticeably. It is also known that the resistance of the Hall Effectsensor varies with temperature. Because the measurement is directlyrelated to the resistance of the Hall Effect sensor, a change intemperature would result in a change in the Hall Effect resistance and achange in the result of the magnetic measurement. This is also calledmeasurement drift due to temperature.

An existing effort made in an attempt to reduce this effect was tore-calibrate the instrument whenever the instrument is in a conditioncalled “Ball-Off condition”, i.e. whenever there are no targets. Byre-calibrating, adjustment is made so that the sensor is calibrated tothe current testing conditions, including temperature. However, sincethis Ball-Off condition does not always occur, or occur frequentlyenough, the measurement could drift with temperature change without theknowledge of measurement taker or operator.

Another existing effort has been seen in U.S. Pat. No. 5,055,768 inwhich a temperature sensitive current source is deployed to solve theproblem of Hall effect sensor sensitivity to temperature. This currentsource is intended to be part of the Hall effect sensor. However, thecircuit as disclosed is limited to compensating temperature effectsinside the Hall sensor residing on the same chip.

Yet another existing effort seen in U.S. Pat. No. 6,281,679 involves asystem that uses a magnet and a Hall Effect sensor to measure distance.However, the magnets and the Hall sensor move in relation to each other.It teaches a method by which two Hall sensors are matched so thattemperature is not a factor. It also addresses methods of regulating thetemperature of the magnet and Hall sensors by auxiliary temperaturecontrol, including using circulated air. Yet, it failed to mention thechallenge brought by and hence the solution to the issue of temperaturevariation between the locals of Hall probe and the processing circuit,which is located in the instrument.

U.S. Pat. No. 8,274,287 uses a magnet and a Hall sensor to detectdisturbances in the field. It also employs a temperature sensor tocontrol the temperature compensation of its measurement on quantity ofmetallic debris. However, the patent did not make use of the uniqueproperty and the subsequent advantages presented by Hall sensors'sensitivity to temperature. It did not make any effort in measuringchanges of Hall sensors circuitry reading attributed to temperaturechange. In addition, it explicitly regards the temperature response aslinear, which is not an accurate representation of this line of Hallsensor devices.

U.S. Pat. No. 6,154,027A uses a temperature reference circuit to controlthe current flow from a temperature-variable current source to aHall-effect element according to sensed temperature conditions. It in away compensates the temperature drift reflected in the current source.However, it does not, in Applicant's opinion, directly compensate thetemperature effect within the Hall Effect sensor.

In U.S. Pat. No. 4,327,416 ('416), the temperature of the Hall elementis measured by a thermistor to develop a temperature dependent voltage.In one embodiment, the Hall element voltage and temperature dependentvoltage are digitalized and supplied to address the ROM to generate atemperature compensated Hall voltage. In another embodiment, the ROM isaddressed by only the temperature dependent voltage to generate acorrection voltage that is added to the Hall element voltage fortemperature compensation. However, in Applicant's opinion, '416 does nottake into account that the source of temperature change is from both thetemperature drift within the Hall Effect sensor, and within the magneticsource, noting that it only relies on the thermistor to gauge theinstant temperature. In addition, this effort does not use a second pairof voltage measurement from the Hall sensor, which could lead totemperature compensation with higher fidelity.

US Patent 2008/0074108 also relies reading from a temperature sensor tocompensate on Hall Effect measurement. It does not use the voltagemeasurement of a second pair from the Hall Sensor as the basis to thecalculation of temperature effect directly on the Hall Sensor itself,not just on the magnetic fields.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the present disclosure to providea Hall Effect instrument with the capability of compensating fortemperature drift consistently, accurately and in real time ofoperation.

It is another objective of the present disclosure to accurately measurethe Hall Effect sensor resistance via a four-point ohmmeter circuit totrack the effect of temperature on the Hall Effect sensor.

It is yet another objective of the present disclosure to provide a HallEffect instrument configured to constantly measure the change in Hallsensor resistance due to change in temperature and to derive arelationship between the temperature and the compensation index on a perprobe basis, which has exhibited a deterministic difference observed bythe present inventor.

It is yet another objective of the present disclosure to provide a HallEffect instrument configured to make compensation of the measurementresult based on system-wide temperature changes, including temperaturechanges caused by locale distance between the Hall sensor and themagnets, the Hall sensor (Hall probe) the processing circuit (theinstrument), etc.

BRIEF DESCRIPTION TO DRAWINGS

FIG. 1 is a block/flow diagram presenting the Hall Effect instrumentwith Temperature Compensation using a four-wire ohmmeter circuittechnique according to present disclosure.

FIG. 2 is schematic diagram depicting the components of a Hall sensorprobe (101) for thickness measurement embodying a temperature sensoraccording to the present disclosure.

FIGS. 3 a and 3 b are schematic circuit diagrams depicting the two-wireor four-wire ohmmeter circuit, respectively, used in the presentdisclosure to accurately measure the Hall Effect sensor resistance,which is highly sensitive to temperature change.

FIG. 4 is a flowchart depicting a data acquisition and processing module(103). It shows how the measurements taken from a Hall Effect sensor(203) are acquired and processed before the measurements are used fortemperature compensation.

FIG. 5 is a flowchart elaborating a temperature compensation module(104). It further comprises three modules, one for probe parametercompensation and one for slope compensation and the third module forcalculating the Temperature Compensation Index.

FIG. 6 is a flowchart depicting how a probe parameter temperaturecompensation module (501) calculates probe parameter temperaturecompensation, voltage, and V_(COMP) _(—) _(P).

FIG. 7 is a graph showing relationship of V_(COMP) versus Temperature,which is used to determine the temperature compensation slope for theexemplary probe.

FIG. 8 is a flow chart depicting a probe slope temperature compensationmodule (502) calculating probe slope temperature compensation voltageand V_(COMP) _(—) _(S).

FIG. 9 is yet another flow chart representing how a probe temperaturecompensation index calculation module (503) calculates the TemperatureCompensated Index.

FIG. 10 is a flow chart depicting steps through which the TemperatureCompensated Measurement is determined from the Temperature CompensatedIndex.

FIG. 11 is a block/flow diagram presenting an alternative embodiment ofthe Hall Effect instrument with Temperature Compensation using afour-wire ohmmeter circuit technique according to the presentdisclosure.

FIG. 12 is schematic diagram depicting the components of Hall sensorprobe (101) in the alternative embodiment for thickness measurementembodying a temperature sensor according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

It should also be noted that some terms commonly used in the industryare interchangeably used in the present disclosure to denote the HallEffect sensor. For example, “Hall Effect sensor”, “Hall probe” and “Hallsensor”, etc., all denote to the Hall Effect sensor shown as 203 in FIG.2. It should also be noted that “Hall Effect instrument” or “Hall sensorinstrument” denotes to the whole measurement system including the Hallprobe, data acquisition circuitry and the whole logic and processingcircuitry (not shown). Such variations in the usage of these terms donot affect the scope of the present disclosure.

Referring to FIG. 1, a block diagram of the presently disclosedtemperature compensated Hall Effect Sensor Measurement System using afour-wire ohmmeter circuit technique is presented. As can be seen theHall sensor measurement system includes mainly five modules or fivesteps used for compensating measurement drift caused by the effect ofchanges of operational temperature. Each of the five modules is furtherelaborated to provide more details in subsequent figures.

According to FIG. 1, the Hall-Effect measurement instrument withtemperature compensation in the present disclosure comprises a Hallsensor probe 101, a Hall Effect measurement circuit 102, a dataacquisition and processing module 103, a temperature compensation module104 and a measurement conversion module 105.

As can be seen in FIG. 1 that signals acquired by Hall sensor probe 101,including V_(SNS) _(—) _(PIN), V_(MON) _(—) _(PIN) and temperature atthe probe are measured and fed into Hall Effect measurement circuit 102which accurately captures three pairs of differential signals from theHall Effect sensor to produce the three Hall Effect Sensor TemperatureUncompensated Raw Data for data acquisition and processing module 103.The three pairs of differential signals including V_(SNS) _(—) _(PIN),V_(MON) _(—) _(PIN) are further elaborated in the subsequentdescription. Temperature un-compensated data is then sent to temperaturecompensation module 104 which operates to combined thermostat readingfrom Hall sensor probe 101 and the probe slope from an EEPROM 208(described later) and a temperature compensation algorithm to produceTemperature Compensated Index. The measurement conversion module 105then determines the correct Hall Effect measurement, such as correctedthickness, with the information from compensation module 104.

It should be appreciated that the temperature compensation function asnovel aspect of the Hall instrument is largely carried out and executedconcurrently with other normal operational functions of the Hallinstrument, and can be built within the same components that otherwiseserve other functions of the Hall sensor instrument. For instance, Hallsensor probe 101 both serves for Hall Effect measurement and temperaturemeasurement with a temperature sensor 207. Data acquisition andprocessing module mainly serves the processing need for the Hall Effectmeasurement, and also provides the data processing need for temperaturecompensation as described in the present disclosure. In other words, thesteps and or modules embodied in the present disclosure can largelyco-use hardware components of the Hall effect instrument that aredesigned for the main purpose of the Hall Effect measurement, i.e.,thickness measurement.

Optionally, the Hall Effect measurement system can be coupled with twotypes of probes in separate measurement sessions, the first type ofprobes includes temperature sensor 207, the second probe does notinclude any temperature sensor. Accordingly, data acquisition andprocessing module 103 optionally includes a mode selection module 1100,selecting modes between the first type of probes is coupled or thesecond type of probes is coupled. The mode selection can be done eitherautomatically based on probe identification, which is an existingpractice, or manually by means of operator input. The embodiment of themeasurement system to be without temperature sensor 207 is described indetails later associated with FIGS. 11 and 12.

It should also be appreciated that any of the steps or modules shown inFIG. 1 can alternatively resides in and be executed by other stand-aloneor add-on components so that the method of temperature compensation onHall Effect measurement can be used in combination of existing HallEffect instrument. The alternatively devised add-on components are alsowithin the framework of the present disclosure.

Reference now is turned to FIG. 2. According to FIG. 2, the Hallmeasurement system firstly embodies Hall sensor probe 101. Hall sensorprobe 101 further comprises a Hall Effect sensor 203, magnets 206providing the primary magnetic field source, a temperature sensor 207,an electrical erasable type of memory device such as EEPROM 208, and aprobe casing 209.

A thickness measurement is taken by placing Hall sensor probe 101between a nonferrous material to be measured and a target ball 201. HallEffect sensor 203 measures the magnetic field between target ball 201and Hall sensor probe 101. Magnets 206 encased in probe casing 209generate a magnetic field between the probe and the target ball. Thismagnetic field is detected by Hall Effect sensor 203. It then sends theHall Effect sensor measurement signals, the Probe Slope (describedlater) from the EEPROM 208 and the temperature from temperature sensor207 into the data processing circuitry of the measurement systemresiding on the instrument for further processing.

In addition, temperature sensor 207 provides the temperature of themagnets T_(mag) for temperature compensation module 104. Lastly, Hallsensor probe 101 uses memory EEPROM 208 to record the probe specificinformation, such as the Probe Slope (described later) used in thetemperature compensation module 104 and other probe identificationparameters common to existing practice. How the Probe Slope was derivedis subsequently explained in relation to FIGS. 7 a and 7 b.

Referring to FIGS. 3 a and 3 b, Hall Effect measurement circuit 102 canbe devised with two alternative embodiments, one detailed as using afour-wire ohmmeter with a drive current monitoring circuit 310 in FIG. 3a; the other as using a four-wire ohmmeter with a constant currentsource I_(SRC) (without circuit 310) in FIG. 3 b.

According to FIG. 3 a, Hall Effect measurement circuit 102 embodies asub-circuit similar to that of four-wire ohm meter and drive currentmonitoring circuit 310. Hall Effect measurement circuit 102 furtherembodies components producing three pairs of differential Hall Effectsensor signals which are accurately measured to produce threeTemperature Uncompensated Raw Data for data acquisition and processingmodule 103. Hall Effect sensor 203 via Hall Effect measurement circuit102, as shown in FIG. 3 a, produces three pairs of differential signalsfor further processing.

The three differential pairs of Hall Effect Sensor signals are definedas:

-   -   a. V_(SNS) _(—) _(PIN)—Positive Hall Effect Sense        Voltage—positive differential input to an amplifier 302;    -   b. V_(SNS) _(—) _(NIN)—Negative Hall Effect Sense        Voltage—negative differential input to amplifier 302;    -   c. V_(MON) _(—) _(PIN)—Positive Hall Effect Monitor        Voltage—positive differential input to a differential amplifier        304;    -   d. V_(MON) _(—) _(NIN)—Negative Hall Effect Monitor        Voltage—negative differential input to differential amplifier        304;    -   e. V_(IMON) _(—) _(PIN)—Positive Hall Effect Voltage modulated        with current stability, V_(IMON)—positive differential input to        an amplifier 306;    -   f. V_(IMON) _(—) _(PIN)—Negative Hall Effect voltage modulated        with current stability, V_(IMON)—negative differential input to        an amplifier 306.

Continuing to the right-hand side of FIG. 3 a, Hall Effect measurementcircuit 102 produces three Temperature Uncompensated Raw Data outputsdefined as:

-   -   g. V_(SNS) _(—) _(R)—Hall Effect Raw Digital Sense        Voltage—digital output from an analog to digital converter 303;    -   h. V_(MON) _(—) _(R)—Hall Effect Raw Digital Monitor        Voltage—digital output from an analog to digital converter 305;    -   i. V_(IMON) _(—) _(R)—Hall Effect Raw Digital voltage modulated        for current stability, V_(IMOD),—digital output from an analog        to digital converter 307.

It should be noted that the Hall Effect measurement circuit includes asub-circuit that happens to be the same as that used in the existingpractice involving a four-wire ohmmeter. One of the novel aspects of thepresent disclosure is to repurpose the four-wire circuit for Hall Effectmeasurement. The temperature compensation aspect of the operation alsouses the signals retrieved from the four-wire circuit. It can thereforebe understood that the four-wire ohmmeter itself had existed in priorpractice. However, the use of such circuit for Hall Effect measurement,thickness measurement and for further making temperature compensation ofsuch measurements are considered novel by the present disclosure.

Still referring to FIG. 3 a, the methodology involved in the usage ofHall Effect measurement circuit 102 is herein described. Starting at thelower left-hand corner of FIG. 3 a, a (constant) voltage source 309 isused to provide a constant current I_(SRC) that goes across a resistor308. This constant current, I_(SRC), is the same constant current thatgoes across the Hall Effect sensor from Point 3 to Point 4. The constantcurrent, I_(SRC), continues and sinks into an amplifier 301. A constantcurrent, I_(SRC), is provided across the Hall Effect Sensor and a Kelvinconnection at Points 1 and 2 are made to ensure proper and accuratemeasurement of a resistor.

With the accurate measurement of the Hall Effect sensor resistance bymeasuring the voltage across Points 1 and 2, we have V_(MON) _(—) _(PIN)and V_(MON) _(—) _(NIN). These two differential signals, V_(MON) _(—)_(PIN) and V_(MON) _(—) _(NIN), can be measured by connecting them todifferential amplifier 304, followed by analog to digital converter 305.The resultant digital signal, V_(MON) _(—) _(R), represents the voltageacross the Hall Effect sensor.

Continuing with FIG. 3 a, by Ohm's Law, the resistance of the HallEffect sensor can be expressed as V_(MON) _(—) _(R)/I_(SRC). SinceI_(SRC) is a constant current, then V_(MON) _(—) _(R) is proportional tothe resistance of the Hall Effect Sensor. Since the resistance of theHall Effect sensor is also proportional to temperature, we now have ameasurement, V_(MON) _(—) _(R), which is proportional to temperature.This is one of several signals used to compensate measurement due totemperature drift.

Similarly, the Hall Effect sensor voltage, V_(SNS) _(—) _(R), via thedifferential signals, V_(SNS) _(—) _(PIN) and V_(SNS) _(—) _(NIN), aremeasured via amplifier 302, and analog to digital converter 303, toproduce V_(SNS) _(—) _(R).

And the constant current, I_(SRC), via V_(IMOD) _(—) _(PIN) and V_(IMON)_(—) _(NIN) are measured by amplifier 306, and analog to digitalconverter 307, to produce V_(IMOD) _(—) _(R).

Lastly V_(MON) _(—) _(R), V_(SNS) _(—) _(R), V_(IMOD) _(—) _(R), as wellas temperature of the magnets and Probe Slope (later described) can beused to further determine how to compensate for temperature drift.

Reference is now made to FIG. 3 b. An alternative implementation can beviewed by substituting another design for FIG. 3 a. As for theembodiment shown in FIG. 3 a, the origin of V_(IMOD) _(—) _(R) is thevoltage across resistor 308. In this way VIMOD_(—R) monitors theperformance of the constant current drive circuit. Components 301, 308and 309 make a constant current source used to drive a current throughthe Hall Effect sensor 203. If voltage source 309 changes for anyreason, V_(IMOD) _(—) _(R) will detect this and be used to compensatefor the matching changes in Vmon and Vsns.

It should be noted that voltage source 309 can be an AC or DC source,bearing in mind that drive current monitoring circuit 310 is effectivewhen AC is used.

As voltage source 309 does not need to be extremely stable for excellentinstrument performance, V_(IMOD) is used to compensate or performancelimitations of circuits inside the gage only in this preferredembodiment shown in FIG. 3 a. V_(IMOD) does not compensate the probe. Inother words, V_(IMOD) is not a must needed component in order for thesystem in the present disclosure to function as intended. It should beappreciated that with or without the usage of V_(IMOD) and itsassociated components are all within the scope of the presentdisclosure.

As an example, referring to FIG. 3 b, an alternative embodiment is shownto be without V_(IMOD). A constant current source forcing a current Isrcthrough probe casing 209 Point 3 to Point 4. It should be noted thatwhen referring to FIG. 3 b as a replacement for FIG. 3 a, the value Isrccan be used to substitute the use of V_(IMOD) in the subsequentimplementations. In this regard, Isrc can be assumed as a constant,which in an exemplary case, to be about 1 mA.

Reference is now turned to FIG. 4 which presents a more detailed diagramof data acquisition and processing module 103. This module furthercomprises two modules: a data acquisition module 401, and a signalprocessing module 402. Data acquisition module 401 takes in the threeinputs V_(MON) _(—) _(R), V_(SNS) _(—) _(R), and V_(IMON) _(—) _(R) orIsrc from circuits shown in FIGS. 3 a and 3 b, and, through a magnitudedetection circuit, produces three signals, V_(MON) _(—) _(DA), V_(SNS)_(—) _(DA), and I_(DA). In FIG. 4, the three temperature UncompensatedRaw Data from circuits shown in FIGS. 3 a and 3 b are acquired andprocessed to produce the three temperature Uncompensated Filtered Datafor temperature compensation module 104.

Three signals, V_(MON) _(—) _(DA), V_(SNS) _(—) _(DA), I_(DA), then goto signal processing module 402, where they get filtered to producethree final signal magnitudes, V_(MON) _(—) _(F), V_(SNS) _(—) _(F), andV_(IMON) _(—) _(F), for the next stage, temperature compensation module104.

The three Temperature Uncompensated Filtered Data outputs are definedas:

-   -   j. V_(SNS) _(—) _(F)—Hall Effect Filtered Digital Sense        Voltage—filtered output from signal processing module 402;    -   k. V_(MON) _(—) _(F)—Hall Effect Filtered Digital Monitor        Voltage—filtered output from signal processing module 402;    -   l. V_(IMON) _(—) _(F) Hall Effect Filtered Digital V_(IMOD)        Voltage modulated with current stability filtered output from        signal processing module 402.

Reference is now made to FIG. 5, with a more detailed diagram oftemperature compensation module 104 of FIG. 1. Temperature compensationmodule 104 further comprises three modules: probe parameter temperaturecompensation module 501, probe slope temperature compensation module502, and probe temperature compensation index calculation module 503. Inthis stage, the three Temperature Uncompensated Filtered Data, alongwith the magnet temperature reading from temperature sensor 207, and theProbe Slope from EEPROM 208, are used to calculate the TemperatureCompensated Index.

Probe parameter temperature compensation module 501 receives fourinputs: V_(MON) _(—) _(F), V_(SNS) _(—) _(F), and V_(IMON) _(—) _(F)from 103 and temperature (T_(mag)) from temperature sensor 207. Thismodule then produces a first compensation factor V_(COMP) _(—) _(P). Formore details, refer to FIG. 6.

Probe slope temperature compensation module 502 receives two inputs:temperature (T_(mag)) from temperature sensor 207, and Probe Slope fromEEPROM 208. This module 502 then produces a second compensation factorV_(COMP) _(—) _(S). For more details, refer to FIG. 8.

Probe temperature compensation index calculation module 503 receives twoinputs: V_(COMP) _(—) _(P) and V_(COMP) _(—) _(S). This module thenproduces the Temperature Compensated Index. For more details, refer toFIG. 9.

Referring now to FIG. 6, a more detailed diagram of probe parametertemperature compensation module 501 of FIG. 5 is presented. The fourinputs, V_(MON) _(—) _(F), V_(SNS) _(—) _(F), and V_(IMON) _(—) _(F)from 103 and T_(mag) from 207 are received through parameter input 510,and sent to probe parameter temperature compensation calculator 512,which produces the product of probe parameter temperature compensationmodule 501. As can be seen below, probe parameter temperaturecompensation calculator 512 can be configured to carry out calculationsin one of the following two equations, Eq. 1 or Eq. 2.

V _(COMP) _(—) _(P) =V _(SNS) _(—) _(F) +V _(MON) _(—) _(F)*(α+V _(SNS)_(—) _(F)*β)+T _(mag)*(γ+V _(SNS) _(—) _(F)*δ)  Eq. 1

wherein, T_(mag) is the temperature from temperature sensor 207;

α, β, γ and δ are constants based upon the manufacturing tolerances ofHall sensor probe 101. They can be obtained by those skilled in the artaccording to Eq. 1, and empirical data from conducting experiments onthe probe of each probe type, yielding readings of the V_(SNS) _(—)_(F), V_(MON) _(—) _(F), I_(SRC) from the corresponding four-wireohmmeter and the temperature reading, T_(mag), for the probe.

Once V_(COMP) _(—) _(P) is calculated, it goes through a probe parametertemperature voltage output 514, and is sent to probe temperaturecompensation index calculation module 503 of FIG. 5.

As can be seen, the temperature compensation calculation according toEq. 1 reflects temperature changes both in the Hall sensor, throughreading V_(MON) _(—) _(F) and V_(SNS) _(—) _(F), and near the magnets,through T_(mag).

It should be noted that in Eq. 1, it is assumed that I_(SRC) is aconstant and the factor represented by V_(IMON) _(—) _(R) is notreflected in it. Therefore Eq. 1 is suitable to be used for theembodiment presented in FIG. 3 b, wherein the embodiment shown in FIG. 3a does not include a sub-circuit for monitoring the stability ofI_(SRC).

It should be noted in connection to FIG. 3 a that V_(IMON) _(—) _(F) isused to monitor how stable the constant current, I_(SRC), is and tofactor in the stability of I_(SRC) into the temperature compensation.

For the embodiment of the measurement circuit 310 with voltage sourcemonitoring (FIG. 3 a),

V _(COMP) _(—) _(P)=(((V _(SNS) _(—) _(F))+((V _(MON) _(—) _(F) −V_(IMON) _(—) _(F))*A)+(((V _(MON) _(—) _(F) −V _(IMON) _(—) _(F))*(V_(SNS) _(—) _(F))*B)/(V _(IMON) _(—) _(F)))+((T _(mag)−22)*(V _(IMON)_(—) _(F))*C)+((T _(mag)−22)*(V _(SNS) _(—) _(F))*D))/(V _(IMON) _(—)_(F)))  Eq. 2

wherein there are six major contributing parts to V_(COMP) _(—) _(P):

-   i) V_(SNS) _(—) _(F) is the factor involving the Hall Effect    Filtered Digital Sense Voltage;-   ii) ((V_(MON) _(—) _(F)−V_(IMON) _(—) _(F))*A) provides temperature    compensation based on the Hall sensor temperature as indicated by    V_(MON) _(—) _(F), with coefficient A modulating the magnitude of    this portion of the temperature compensation, which is intended to    correct the “ball-off” situation, but has an equal impact on    “ball-on” situation;-   iii) ((V_(MON) _(—) _(F)−V_(IMON) _(—) _(F))*(V_(SNS) _(—)    _(F))*B)/(V_(IMON) _(—) _(F))) is a scalar temperature compensation    factor based on the Hall sensor temperature as indicated by V_(MON)    _(—) _(F), and wherein coefficient B modulates the amount of    correction, which is intended to correct the ball-off situation and    accounts for manufacturing tolerances of the Probe and Hall Effect    sensor;-   iv) ((T_(mag)−22)*(V_(IMON) _(—) _(F))*C) provides offset    temperature compensation based on the magnet temperature as    indicated by T_(mag), and wherein C is the factor involving the    T_(mag) from Temperature Sensor 207 and accounts for the specific    probe manufacturing tolerances;-   v) ((T_(mag)−22)*(V_(SNS) _(—) _(F))*D) provides scalar temperature    compensation based on the magnet temperature as indicated by    T_(mag), and wherein D is a factor involving the T_(mag) from    Temperature Sensor 207 and accounts for the specific probe    manufacturing tolerances.

It should be noted that reference temperature herein used in theequation (22° C.) is an exemplary ambient temperature. Different valuescan be used when calibration is done differently.

A, B, C and D are constants based upon the manufacturing tolerances ofHall sensor probe 101. They can be obtained by those skilled in the artaccording to Eq. 2, and empirical data from conducting experiments onthe probe of each probe type, yielding readings of the V_(SNS) _(—)_(F), V_(MON) _(—) _(F), V_(IMON) _(—) _(F) from the correspondingfour-wire ohmmeter and the temperature reading T_(mag) for the probeused in the experiment.

Once the V_(COMP) _(—) _(P) is calculated, it goes through probeparameter temperature voltage output 514, and is sent to probetemperature compensation index calculation module 503.

Again it can be noted that Eq. 1 compensates measurement inaccuraciesdue to temperature drift quite well without using the factor related toV_(IMON) _(—) _(F). V_(IMON) _(—) _(F) is used solely to monitor howstable the constant current I_(SCR) is.

Eq. 2 provides better temperature compensation taking into account whenI_(SCR) varies. In addition, measurement variation due tointerdependencies between the four inputs (V_(SNS) _(—) _(F), V_(MON)_(—) _(F), V_(IMON) _(—) _(F), Temperature) are compensated via Eq. 2'sfactors ii) through v).

Reference is now made to FIG. 7 which present a methodology hereinemployed to determine the per probe relationship between Temperature andV_(COMP) slope called V_(COMP-S).

FIG. 7 represents an exemplary probe-specific slope drawing by usingexperimental data from a case collected from the probe for varioustemperature settings. The exemplary Hall Effect measurement circuit forthe specific probe as shown in FIG. 3 a is measured with varioustemperatures. V_(MON) _(—) _(F), V_(SNS) _(—) _(F) and V_(IMON) _(—)_(F) are drawn from the measurement and V_(COMP) _(—) _(P) is calculatedby using Eq. 2. FIG. 7 is then plotted representing the relationshipbetween Temperature and V_(COMP) _(—) _(S).

The Probe Slope derived from the experimental data graph similar to FIG.7 using a linear curve fit is stored in EEPROM 208, to be retrieved forFIG. 8.

FIG. 8 presents a more detailed diagram of probe slope temperaturecompensation module 502.

In parallel to the calculation of V_(COMP) _(—) _(P), V_(COMP) _(—) _(S)is calculated in this module. The Probe Slope, from EEPROM 208, and themagnet's temperature from temperature sensor 207, are received through aparameter input 520, and sent to probe slope temperature compensationcalculator 522. The calculator used is in the following format:

V _(COMP) _(—) _(S)=Probe Slope*(T _(mag)−Reference Temperature)  Eq. 3

-   -   where V_(COMP) _(—) _(S) adjusts the overall V_(COMP) based upon        the probe's response to magnet's temperature.

Once V_(COMP) _(—) _(S) is calculated, it goes through a probe slopetemperature voltage output 524, and is sent to probe temperaturecompensation index calculation module 503.

FIG. 9 presents a more detailed diagram of probe temperaturecompensation index calculation module 503.

The V_(COMP) _(—) _(P) from 501 and V_(COMP) _(—) _(S) from probe slopetemperature compensation module 502 are received through a parameterinput 530, and sent to a temperature compensated index calculator 532.The calculator used is in the following format:

Temperature Compensation Index=V _(COMP) _(—) _(P) −V _(COMP) _(—)_(S)  Eq. 4

Once the Temperature Compensated Index is calculated, it goes through atemperature compensated index output 534, and is sent to measurementconversion module 105.

FIG. 10 provides a more detailed exhibit of measurement conversionmodule 105 showing how the temperature compensated thickness measurementis converted from the Temperature Compensated Index. In order to use thetemperature compensated index V_(comp) (right column in FIG. 10) for aspecific probe, a specific target is used in experiments to derivemeasured thickness at the reference ambient temperature (22° C.).

Temperature Compensated Index, or compensated Hall Effect readingV_(comp), is then fed into measurement conversion module 105 andconverted by a probe-target specific conversion, such as shown in FIG.10. It is known to those skilled in the art to obtain empirical databetween a Hall Effect reading and a thickness measurement for anyspecific set of probe and target. The novel aspect of the inventionherein presented is that the effect of temperature change to Hall Effectreading is compensated and presented as “compensated index V_(comp)”.The temperature compensated or corrected measurement (thickness) istherefrom accurately produced. In the exemplary conversion used in FIG.10, Temperature Compensated Index V_(comp) is provided to measurementconversion module 105. Based on the V_(comp) and through linearinterpolation, an accurate measurement is produced by measurementconversion module 105.

Reference now is made to FIGS. 11 and 12 which present an alternativeembodiment in the present Continuation-in-Part application.

The alternative embodiment herein presented shares the same principle aspresented in the parent co-pending U.S. application Ser. No. 14/077,322of providing accurately measure the Hall Effect sensor resistance via afour-point ohmmeter circuit to track the effect of temperature on theHall Effect sensor. However, as shown in FIGS. 11 and 12, thealternative embodiment of the Hall Effect sensor does not use, nordepend on the usage of a temperature sensor, such as temperature sensor207 as shown in FIGS. 1 and 2.

Therefore, as shown in FIGS. 11 and 12, and in FIGS. 3 a, 3 b, 4˜10, thealternative embodiment of the Hall Effect measurement instrument withtemperature compensation in the present Continuation-in-part disclosurecomprises Hall sensor probe 101, Hall Effect measurement circuit 102,data acquisition and processing module 103, temperature compensationmodule 104 and measurement conversion module 105. Probe 101 furthercomprises Hall Effect sensor 203, magnets 206 providing the primarymagnetic field source, an electrical erasable type of memory device suchas EEPROM 208 and probe casing 209.

In this alternative embodiment, Hall Effect measurement circuit 102 isthe same as that of in the co-pending U.S. application Ser. No.14/077,322. For temperature compensation module 104, there is no signalfeed from a temperature sensor. Therefore, for this alternativeembodiment, there is no temperature sensor 207 and its associatedtemperature signal feed in FIGS. 5, 6, 7, 8 and 9.

Subsequently, for this alternative embodiment without magnet temperaturesensor, Eq. 1 is changed to:

V _(COMP) _(—) _(P) =V _(SNS) _(—) _(F) +V _(MON) _(—) _(F)*(α+V _(SNS)_(—) _(F)*β)  Eq. 5

wherein, α, β, γ and δ are constants based upon the manufacturingtolerances of probe 101. They can be obtained by those skilled in theart according to Eq. 3, and empirical data from conducting experimentson the probe of each probe type, yielding readings of the V_(SNS) _(—)_(F), V_(MON) _(—) _(F), I_(SRC) from the corresponding four-wireohmmeter in FIGS. 3 a and 3 b.

Further for this alternative embodiment without magnet temperaturesensor, for circuit 310 in FIGS. 3 a and 3 b, constant coefficients Cand D are both zero in Eq. 2.

It should be appreciated by those skilled in the art that variousimplementations can be achieve for embodiments with or without the usageof magnet temperature sensor. All of such implementations are within thescope of the present disclosure.

For example, one can design the Hall Effect measurement instrument bycoding data acquisition and processing module 103 with only one set ofequations Eq. 1 to 4 for both embodiments suiting for probes with orwithout the magnet temperature sensor, providing an option-toggle key ofeither a virtue or physical button allowing users to choose between theembodiments. The toggle function can also be automatically triggeredonce the probe is plugged in based on the probe identification, which isan existing practice to those skilled in the art. When option is chosento be without the magnet temperature sensor, the coefficient C and D areset to zero in Eq. 2, and T_(mag) is automatically set to be 22° C. inEq. 3. The toggle function can be implemented by mode selection module1100 described in association with FIG. 1.

It should be noted that usually when Hall sensor probes are relativelysmall with smaller magnets for applications of making thickness gages onthinner material, the temperature difference between the end of magnetsand the tip of the Hall sensor can be negated. In this case, a Hallsensor probe without magnet temperature sensor can be used.

An alternative example would be for one to design the Hall Effectmeasurement instrument only for using probes without magnet temperaturesensor. In this case, Eqs. 1-4 are correspondingly modified as followsand coded to data acquisition and processing module 103.

V _(COMP) _(—) _(P) =V _(SNS) _(—) _(F) +V _(MON) _(—) _(F)*(α+V _(SNS)_(—) _(F)*β)  Eq. 5 (corresponding to Eq. 1)

V _(COMP) _(—) _(P)=(((V _(SNS) _(—) _(F))+((V _(MON) _(—) _(F) −V_(IMON) _(—) _(F))*A)+(((V _(MON) _(—) _(F) −V _(IMON) _(—) _(F))*(V_(SNS) _(—) _(F))*B)/(V _(IMON) _(—) _(F)))  Eq. 6 (corresponding to Eq.2)

Temperature Compensation Index=V _(COMP) _(—) _(P)  Eq. 7 (correspondingto Eq. 4)

Subsequently, there is no input or consideration for V_(comp) _(—) _(S)and there is therefore no equation corresponding to Eq. 3 for theembodiment of without magnet temperature sensor.

Further, for the instrument designed only for probes without magnettemperature sensor, the following elements are removed from dataacquisition and processing module 103 in the following manner:

-   -   in FIG. 5, temperature sensor input from temperature sensor 207,        probe slope temperature compensation module 502 and input        V_(COMP) _(—) _(S);    -   in FIG. 6, temperature input from temperature sensor 207;    -   in FIG. 7, the probe slope;    -   in FIG. 8, temperature input from temperature sensor 207;    -   in FIG. 9, V_(COMP) _(—) _(S);

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention not be limited by thespecific disclosure herein.

What is claimed is:
 1. An instrument measuring Hall Effect of at leastone Hall sensor magnetically coupled with a target during a measurementsession, comprising: a probe including the Hall sensor and a magneticfield source, a data processing and display console coupled with theprobe with an electronic coupling means, the console further comprising,a Hall Effect measurement circuit connected with the Hall sensor via thecoupling means, the Hall Effect measurement circuitry further includingat least partially a four-wire ohmmeter circuit, which captures at leasttwo pairs of differential signals from the Hall Effect sensor, a dataacquisition and processing module configured to receive signals from theHall Effect measurement circuit and provide at least two pairs ofuncompensated raw signals based on the differential signals; atemperature compensation module configured to compute based on the atleast two pairs of uncompensated raw data to produce a temperaturecompensation index; a measurement conversion module configured toprovide a corrected Hall Effect measurement data by correcting the rawsignal data using information corresponding to the temperaturecompensation index.
 2. The instrument of claim 1 further comprises anelectronic erasable memory for storing specific information in theprobe.
 3. The instrument of claim 1 is configured to measure thicknessaccording to the strength of the Hall Effect measurement.
 4. Theinstrument of claim 1, wherein the compensation index is a result ofdynamically compensating the Hall Effect measurement of the probe withthe temperature change in the Hall sensor.
 5. The instrument of claim 1,wherein the two pairs of the uncompensated raw data, including raw HallEffect Sense Voltage, V_(SNS) _(—) _(R) and raw Hall Effect MonitorVoltage, V_(MON) _(—) _(R), respectively, wherein V_(SNS) _(—) _(R) andV_(MON) _(—) _(R) is each fed to the data acquisition and processingmodule.
 6. The instrument of claim 5 wherein the data acquisition andprocessing module further comprises a data acquisition module and asignal processing module, wherein the signal processing module producingHall Effect filtered digital sense voltage V_(SNS) _(—) _(F) from theV_(SNS) _(—) _(R) and filtered digital monitor voltage V_(MON) _(—) _(F)from the V_(MON) _(—) _(R).
 7. The instrument of claim 6, wherein thetemperature compensation module further comprises a probe parametertemperature compensation module producing a first compensating factorV_(COMP) _(—) _(P) and a probe temperature compensation indexcalculation module producing a temperature compensation index V_(COMP).8. The instrument of claim 6, wherein the Hall Effect measurementcircuitry further comprises a voltage source providing substantiallyconstant current source I_(SRC) to the four-wire ohmmeter circuit. 9.The instrument of claim 8, wherein the probe parameter temperaturecompensation module further comprises probe parameter temperaturecompensation calculator producing the factor V_(COMP) _(—) _(P)substantially according to the following:V _(COMP) _(—) _(P) =V _(SNS) _(—) _(F) +V _(MON) _(—) _(F)*(α+V _(SNS)_(—) _(F)*β)  Eq. 5
 10. The instrument of claim 9, wherein α and β areobtained according to Eq. 5, and empirical data from conductingexperiments on the probe of each probe type, yielding readings of theV_(SNS) _(—) _(F), V_(MON) _(—) _(F), I_(SRC) from the correspondingfour-wire ohmmeter.
 11. The instrument of claim 7, wherein the HallEffect measurement circuitry further comprises a voltage source and avoltage source current stability monitoring circuit, providing a rawvoltage differential data V_(IMON) _(—) _(R) factored by the currentmonitoring circuit, wherein V_(IMON) _(—) _(R) is further provided tothe data acquisition and processing module.
 12. The instrument of claim11, wherein the signal processing module further provides a filtereddifferential voltage data V_(IMON) _(—) _(F) factored by the currentmonitoring circuit, based on the Hall Effect measurement value of rawvoltage V_(IMON) _(—) _(R).
 13. The instrument of claim 12, wherein theprobe parameter temperature compensation module further comprises an aprobe parameter temperature compensation calculator producing the factorV_(COMP) _(—) _(P) substantially according to the following:V _(COMP) _(—) _(P)=(((V _(SNS) _(—) _(F))+((V _(MON) _(—) _(F) −V_(IMON) _(—) _(F))*A)+(((V _(MON) _(—) _(F) −V _(IMON) _(—) _(F))*(V_(SNS) _(—) _(F))*B)/(V _(IMON) _(—) _(F)))  Eq. 6 wherein A and B areall coefficient accounting for manufacturing tolerances of the probe andthe Hall Effect sensor.
 14. The instrument of claim 8, wherein thetemperature compensation index calculation module calculates thetemperature compensation index, deriving from the first compensationfactor V_(COMP) _(—) _(P) according toTemperature Compensation Index V _(COMP) =V _(COMP) _(—) _(P)  Eq. 7 15.The instrument of claim 14, wherein the measurement conversion module isconfigured to produce the corrected Hall Effect measurement data basedon the temperature compensation index V_(COMP) for the probe and thetarget.
 16. An instrument measuring Hall Effect of at least one Hallsensor magnetically coupled with a target during a measurement sessionand a first probe including the Hall sensor and a first magnetic fieldsource, or a second probe including the Hall sensor, a magnetic fieldsource and a temperature sensor, a data processing and display consolecoupled with the first or the second probe, one at a time, with anelectronic coupling means, the console further comprising, a Hall Effectmeasurement circuit connected with the first or the second Hall sensorrespectively via the coupling means, the Hall Effect measurementcircuitry further including at least partially a four-wire ohmmetercircuit, which captures at least two pairs of differential signals fromthe Hall Effect sensor, a data acquisition and processing moduleconfigured to receive signals from the Hall Effect measurement circuitand provide at least two pairs of uncompensated raw based on thedifferential signals; a mode selection module operable to be switched toa first mode or a second mode corresponding either the first probe orthe second probe is coupled; a temperature compensation moduleconfigured to compute based on the at least two pairs of uncompensatedraw data and the temperature reading and a probe slope associated withthe probe to produce a temperature compensation index; a measurementconversion module configured to provide a corrected Hall Effectmeasurement data by correcting the raw signal data using informationcorresponding to the temperature compensation index.
 17. The instrumentof claim 16 further comprises an electronic erasable memory for storingspecific information in the probe.
 18. The instrument of claim 16,wherein the compensation index is a result of dynamically compensatingthe Hall Effect measurement of the probe with the temperature change inthe Hall sensor and/or at the magnetic source.
 19. The instrument ofclaim 16, wherein the two pairs of the uncompensated raw data, includingraw Hall Effect Sense Voltage, V_(SNS) _(—) _(R) and raw Hall EffectMonitor Voltage, V_(MON) _(—) _(R), respectively, wherein V_(SNS) _(—)_(R) and V_(MON) _(—) _(R) is each fed to the data acquisition andprocessing module, and the data acquisition and processing modulefurther comprises a data acquisition module and a signal processingmodule, wherein the signal processing module producing Hall Effectfiltered digital sense voltage V_(SNS) _(—) _(F) from the V_(SNS) _(—)_(R) and filtered digital monitor voltage V_(MON) _(—) _(F) from theV_(MON) _(—) _(R), and, the temperature compensation module furthercomprises a probe parameter temperature compensation module producing afirst compensating factor V_(COMP) _(—) _(P), a probe slope temperaturecompensation module producing a second compensation factor V_(COMP) _(—)_(S) and a probe temperature compensation index calculation moduleproducing a temperature compensation index V_(COMP), and, the HallEffect measurement circuitry further comprises a voltage source and avoltage source current stability monitoring circuit, providing a rawvoltage differential data V_(IMON) _(—) _(R) factored by the currentmonitoring circuit, wherein V_(IMON) _(—) _(R) is further provided tothe data acquisition and processing module, and, the signal processingmodule further provides a filtered differential voltage data V_(IMON)_(—) _(F) factored by the current monitoring circuit 310, based on theHall Effect measurement value of raw voltage V_(IMON) _(—) _(R), and,the probe parameter temperature compensation module further comprises ana probe parameter temperature compensation calculator producing thefactor V_(COMP) _(—) _(P) substantially according to the following:V _(COMP) _(—) _(P)=(((V _(SNS) _(—) _(F))+((V _(MON) _(—) _(F) −V_(IMON) _(—) _(F))*A)+(((V _(MON) _(—) _(F) −V _(IMON) _(—) _(F))*(V_(SNS) _(—) _(F))*B)/(V _(IMON) _(—) _(F)))+((T _(mag)−22)*(V _(IMON)_(—) _(F))*C)+((T _(mag)−22)*(V _(SNS) _(—) _(F))*D))/(V _(IMON) _(—)_(F)))  Eq. 2 wherein A, B, C and D are all coefficient accounting formanufacturing tolerances of the probe and the Hall Effect sensor, and,the probe parameter temperature compensation module further comprises aprobe slope temperature compensation calculator producing the factorV_(COMP) _(—) _(S) according to a probe slope derived according toexperimental data collected on the probe,V _(COMP) _(—) _(S)=Probe Slope*(T _(mag)−Reference Temperature)  Eq. 3and, the temperature compensation index calculation module calculatesthe temperature compensation index, deriving from the first compensationfactor V_(COMP) _(—) _(P) and the second compensation factor V_(COMP)_(—) _(S) according to,Temperature Compensation Index V _(COMP) =V _(COMP) _(—) _(P) −V _(COMP)_(—) _(S)  Eq. 4 and, the measurement conversion module is configured toproduce the corrected Hall Effect measurement data based on thetemperature compensation index V_(COMP) _(—) _(P) for the first probe orthe second probe and the target.
 20. The instrument of claim 19, whereinwhen the mode selection module is switched to the first mode when thefirst probe is coupled with the instrument, T_(mag)=referencetemperature in Eq. 2, and constant coefficients in Eq. 2, C=0, and D=0.